1. Field of the Invention
The present invention relates to a total organic carbon meter for measuring TOC (total organic carbon) or TC (total carbon) in an aqueous sample.
2. Description of the Background Art
In a case of measuring TOC in an aqueous sample with a TOC meter, it is one of important matters that TOC measurement for carbon concentration of not more than 50 ppb (hereinafter referred to as 50 ppbC) is possible in the TOC test method which is defined in the Pharmacopeia of Japan, for example. According to the revised GMP rule enforced on Apr. 1, 1994, medicinal makers must control TOC values of water for injection water and wash water. When a TOC meter is used for the purpose of TOC control, the user must prove that the TOC meter can measure TOC values of not more than 50 ppbC. Following prevalence of the ISO 9000 standard, a TOC meter which is used for controlling TOC in pure water must be capable of measuring TOC values of ultralow concentration also in other fields, similarly to the above.
In order to prove that a TOC meter can measure TOC values of not more than 50 ppbC, it is necessary to prepare a TOC test solution having known concentration of not more than 50 ppbC. However, it is almost impossible for the user to prepare a solution of such low carbon concentration, for the following reasons:
(1) It is difficult to obtain pure water of not more than 50 ppbC itself.
(2) Even if such pure water can be obtained, it is difficult to prepare and keep a test solution having concentration of not more than 50 ppbC in excellent accuracy, due to contamination exerted from the exterior during preparation of the test solution.
An object of the present invention is to enable a user to prove that a TOC meter has measurement sensitivity for ultralow concentration by enabling preparation of a test solution of ultralow concentration in the interior of the TOC meter.
The TOC meter to which the present invention is directed at least comprises a reaction part at least including a TC oxidative reaction part for converting TC in an aqueous sample to CO2, an automatic sample injector for collecting the aqueous sample or ordinary pure water and injecting the same into the reaction part, a sample injection control part for controlling the sample injecting operation of the automatic sample injector, a carrier gas supply part for supplying carrier gas to the reaction part, a CO2 detection part for detecting CO2 which is received from the reaction part with the carrier gas, and a data processing part for processing a detection signal of the CO2 detection part. According to the present invention, the TOC meter further comprises an ultrapure water trap mechanism which is provided in a passage between the TC oxidative reaction part of the reaction part and the CO2 detection part for retaining condensed water of water vapor which is formed in the TC oxidative reaction part, and a passage for connecting the automatic sample injector with an ultrapure water trap of the ultrapure water trap mechanism to be capable of collecting ultrapure water from the ultrapure water trap and injecting the same into the reaction part. The sample injection control part is also adapted to control an operation of collecting the ultrapure water and ordinary pure water which is outside this apparatus for diluting the ordinary pure water with the ultrapure water and injecting the diluted pure water into the reaction part.
In a preferred mode shown in FIG. 2, the data processing part 13 comprises a calibration curve part 30 for forming and holding calibration curve data, a carbon concentration calculating part 31 for calculating carbon concentration from the detection signal of the CO2 detection part 12 through the calibration curve, and a dilution magnification calculating part 32 for calculating a dilution magnification for forming a test solution having ultralow carbon concentration by diluting the ordinary pure water with the ultrapure water stored in the ultrapure water trap 22 from the concentration calculated by the carbon concentration calculating part 31 in measurement of the ordinary pure water which is outside this apparatus, and the sample injection control part 18 controls to collect the ordinary pure water and the ultrapure water in accordance with the dilution magnification calculated by the dilution magnification calculating part 32 and inject the same into the reaction part 2.
According to the present invention, condensed water of water vapor which is formed in the TC oxidative reaction part is collected in the TOC meter. Since this condensed water is ultrapure water whose TOC value is substantially zero, it is possible to prove that the TOC meter has sensitivity for ultralow concentration by diluting the ordinary pure water (at least 100 ppbC in general), which is subjected to measurement of concentration, with the ultrapure water for preparing a test solution of ultralow concentration and measuring the test solution. Thus, the test solution of ultralow concentration can be prepared in the TOC meter according to the present invention, whereby it is possible to simply measure a test solution of ultralow concentration in high accuracy.